1. Field of the Invention
The embodiments of the invention are directed to reducing core loss and stray load loss in magnetic circuits comprising laminated metallic cores with air gaps between them. More particularly, at least some embodiments of the invention are directed to systems that reduce losses caused by eddy currents in shorted metallic laminations of magnetic circuits.
2. Description of the Related Art
Electric motors, and other devices comprising magnetic circuits where magnetic flux crosses an air gap, utilize stacked metallic laminations as part of the low reluctance path for magnetic flux created by electrical current flow. Metal is used for its low reluctance (resistance to magnetic flux flow) properties, and stacked laminations are used to reduce eddy current losses.
FIG. 1 illustrates the stacked laminations of a stator of an electric motor of the related art. In particular, the stator 10 comprises a plurality of laminations 12 (only some of which are numbered in FIG. 1). Each lamination comprises two or more teeth 14 which define a slot 16 between them. Windings (e.g., copper wiring or bars) are placed within the slots, and teeth 14 form a part of the low reluctance path for the magnetic flux through the stator 10.
Likewise, FIG. 2 illustrates a rotor 20 of an electrical motor of the related art comprising a plurality of stacked laminations 22 (only some of which are numbered in FIG. 2). Each lamination 22 comprises one or more teeth 24 that define a slot 26 between them. Windings (e.g., copper wiring or bars) are placed within the slots 26, and teeth 24 form a part of the low reluctance path for the magnetic flux through the rotor 20.
The rotor 20 of FIG. 2, its main rotational shaft (not shown), and windings (not shown), are placed within the illustrative stator 10 of FIG. 1, and the interactions of the electric and magnetic fields produce rotation when the overall assembly is used as a motor, and produce power if the assembly is used as a generator.
Inasmuch as the rotor 20 turns within the stator 10, the laminations 12 of the stator preferably do not touch the laminations 22 of the rotor 20. Thus, there exists an air gap between the rotor 20 and the stator 10 that the magnetic flux crosses to complete the magnetic circuit. FIG. 3, taken substantially along line 3-3 of FIG. 1, illustrates the relationship of two teeth of the stacked laminations with the upper portion of the teeth bordering the air gap. In particular, a first tooth 30 may comprise a metallic portion 32, along with an insulating layers 34 disposed on each side of the metallic portion 32. Likewise, tooth 36 may comprise a metallic portion 38 surrounded by insulating layers 40. The insulating layers 34 and 40 are used to electrically isolate the laminations to reduce the occurrence of eddy currents in the lamination.
The laminations themselves are made on an individual basis, possibly by stamping the laminations from a larger sheet of material, or by laser cutting the laminations from the larger sheet of material. Regardless of the mechanism by which an individual lamination (e.g., 12 or 22) is made, there is a tendency in the stamping and/or cutting process to create a barb or burr at the edges of each lamination. Referring again to FIG. 3, tooth 30 is shown to have a burr 42 which could be caused, for example, by a die stamping (in the direction indicated by arrow 44) a larger sheet of material to produce the individual lamination. Likewise, tooth 36 illustrates a burr 46 created during its construction. The insulating layers 34 and 40 are added prior to creation of the individual lamination, and therefore stamping or cutting to create a lamination electrically exposes ends of the teeth, for example end 48. In the process of stacking the individual laminations to form the stator and/or rotor, the burrs (e.g., 42 and 46) tend to physically touch the uninsulated area of the adjacent tooth. This creates an electrical conduction path that spans two or more teeth, which thereby increases the eddy current path length and the power loss associated with the eddy currents.
There have been attempts in the related art to reduce the electrical shorting caused by the burrs contacting electrically exposed areas, but these attempts significantly increase manufacturing costs. For example, one related art method is to remove the burrs from each individual lamination after its creation. A second related method is to flame treat the laminations, either individually or after their stacking, in an attempt to burn away the burr material. Yet another related art method is to mill the laminations slightly after staking, also known as a skin cut.
Thus, what is needed in the art is a method and related system to reduce the effects the burrs on each lamination may have without unduly complicating or adding expense to the motor manufacturing process.